The invention relates to a multi-phase extractor having at least two chambers which are connected at their upper and lower parts by connection ducts, are equipped with dispersing devices and comprise ports for the supply and removal of a first, second and optionally third dispersed phase.
A multi-phase extractor of this type may be used in chemical, hydrometallurgical, microbiological and other branches of industry for separating, extracting, concentrating and purifying substances.
Apparatuses for carrying out processes of three-phase fluid extraction are known in the form of a two-chamber system, wherein the two chambers are connected together at the upper part or comprise a porous partition. The chambers are filled with a continuous phase, through which two dispersed phases, which are not soluble in the continuous phase, are passed in the form of drops. This results in the transfer of substances from one dispersed phase (raffinate phase) via the continuous phase (also known as the liquid membrane phase) into the other dispersed phase (extract phase) (c.f. for example Journal xe2x80x9cTheoretische Grundlagen der chemischen Technologiexe2x80x9d 1984, Vol. 18; No. 6, pp. 736-738).
These apparatuses are in need of improvement with respect to their performance and their extension to multistage processes.
From a technical point of view, as well as from that of the achievable effect, the three-phase extractor, which consists of a first and second chamber filled with the continuous phase (liquid membrane), is closest to the known apparatuses. The chambers have devices for dispersing the respective phase and are connected together by overflows for circulation of the continuous phase. The overflows take the form of pipes which connect together the upper and lower parts of the chambers. The extractor is provided with ports for the supply and removal of the first and second dispersed phases (Russian patent application no. 94-015776/26 (015406) of 27.04.94).
The phase to be dispersed, i.e. the initial solution, and the solvent (extract phase) are each dispersed into droplets in the appropriate chamber by means of a dispersing device, said droplets moving together through the continuous phase. Owing to the difference in density between the emulsions in the first and second chamber, circulation of the continuous phase occurs via the upper and lower overflows, resulting in transfer of the substance to be extracted from one chamber to the other and from the first phase to be dispersed into the second.
A disadvantage of the known three-phase extractor resides in the fact that droplets of the dispersed phase may be entrained from one chamber to the other by the circulating continuous phase. This phenomenon, which results in a reduction in the efficiency of the apparatus and to contamination of the extract phase, is reinforced in particular if the ratio between the flow rates of the raffinate phase and the extract phase increases as a result of an increase in circulation momentum (difference between the densities of the emulsions in the first and second chambers).
Another disadvantage is that it is impossible to carry out continuous multi-component extraction in this extractor, i.e. the extractor cannot be used for processes in which selective separation of multi-component mixtures is required (isolation of individual components from an initial solution).
In the case of the extraction and concentration of substances from dilute solutions, e.g. metals from waste waters, the ratio of the flows of the raffinate and the extract may be higher than 2-10. The design of the known extractor does not permit any increase in efficiency in such instances.
The object of the invention is to improve the efficiency of the multi-phase extractor. A further object of the invention is to develop a multi-phase extractor for carrying out continuous multi-component extraction.
Starting with the above-described apparatus, this object is achieved according to the invention in that the two chambers in the multi-phase extractor comprise separation zones, which are located in the area of the inlet openings for the connection ducts.
According to a preferred embodiment, the second chamber is connected at its upper and lower parts with a third chamber.
The chambers are advantageously accommodated in a housing and separated by a common partition.
A modification of the invention is characterised in that, beneath a first stage with the chambers connected at their upper and lower parts, there are arranged further stages connected in series and having interconnected chambers, wherein the individual stages are connected together by means of perforated plates (sieve plates) through which the dispersed phases flow.
The multi-phase extractor is preferably provided with connecting pipes in the perforated plates to convey the continuous phase between the individual stages and with ports in the housing for supply and removal of the continuous phase.
The embodiment comprising separation zones or separating chambers arranged in the area of the inlet openings of the connecting ducts or overflows prevents the circulating flow of the continuous phase from entraining droplets from one chamber to the other. The arrangement of the two chambers in a housing subdivided by a common partition also contributes to this. In this instance, the cross sections of the connecting ducts constructed as overflows is substantially increased and the flow rate of the continuous phase at the transition from one chamber to the other decreased.
The connection of the second chamber with the third provides a fundamentally novel multi-chamber system with a common central second chamber. In conjunction with the ports for the inlet and removal of the third dispersed phase and the dispersing devices, this design permits the implementation of continuous multi-component extraction processes.
The connection between the chambers at their upper and lower ends permits the implementation of various technological variants of the process. For example, the second phase to be dispersed may be used as the initial solution. The components separated therefrom then transfer via the continuous phase into the first and third dispersed phases. Alternatively, the initial mixture may be supplied in the form of the continuous phase, wherein the various components of this continuous phase are extracted via the various dispersed phases.
The additional arrangement of chamber of like design below the first and second chamber (series connection of several stages) permits the implementation of multistage substance separation processes in the multi-phase extractor. The embodiment of the extractor with ports for the supply and removal of the continuous phase and connection pipes to convey it between the stages establishes the prerequisites for the implementation of separation processes by means of the liquid membrane method and three-phase extraction.
FIGS. 1-3 are schematic representations of three possible variants of the three-phase extractor according to the invention and
FIGS. 4-6 show further embodiments of a multi-phase extractor.
FIG. 1 shows a single-stage extractor for carrying out processes for separating substances by means of a circulating continuous phase of fixed location, which acts as a liquid membrane.
FIGS. 2 and 3 are multi-stage three-phase extractors, in which the chambers are accommodated in a housing.